Two best methods in this instance (as far as I'm concerned) would be:

1. buy the morph magnet sets by (I think) Netherworkis, available at DAZ. These are only for specific characters, and can be time consuming if you've used a lot of dials in your character's creation. Basically, you add a set of magnets to the clothing which help it to adjut shape to your character. AS I said, though, these are character specific - V4's magnets only work on V4 clothing, and not on any other characters - so they are not going to work when trying to fit a piece of clothing to A3, for example.  So...

2. Buy Wardrobe Wizard 2, by PhilC. This works incredibly well at taking clothes designed for pretty much any character, and converting them over to another character of your choice. Note here that you do need to have the relevant data for the converting character, purchased in data packs from PhilC (at one point these were given free, but I don't know what the costs are now). It's a much more versatile tool, and is probably the best of the converters out there.

So in the end, it depends whether you're aim is to convert clothing only one specific character (all of V4.2's wardrobe to a specific V4 character you're using, for example) or convert from a wide range to a wide range of characters. Personally, just beause yuo never know what you're going to be using in the future, I'd recommend Wardrobe Wizard even if your scope is at present a little smaller - his customer service is excellent, and it's such a versatile program.

JonTheCelt